Cryogenic fuel semi-closed recirculating bottoming cycle

Abstract

An aircraft propulsion system includes a cryogenic fuel system and a fuel flow path where a fuel flow is circulated from upstream in a direction downstream to a combustor of the core engine. A first heat exchanger inputs heat into the fuel flow downstream of the first heat exchanger is used to heat the fuel flow from the fuel storage tank and a second heat exchanger inputs thermal energy from a heat source into the fuel flow from the core engine downstream of the first heat exchanger. A turboexpander is configured to generate shaft power from expansion of the fuel flow exhausted downstream from at least one of the first heat exchanger and the second heat exchanger.

What is claimed is: 
     
         1 . An aircraft propulsion system comprising:
 a core engine comprising a combustor where a cryogenic fuel is mixed with compressed air and ignited to generate an exhaust gas flow;   a propulsive fan driven by shaft power generated by the core engine;   a cryogenic fuel system comprising a cryogenic fuel storage tank;   a fuel flow path where a fuel flow is circulated from upstream in a direction downstream to the combustor of the core engine;   a first heat exchanger where heat input into the fuel flow downstream of the first heat exchanger is used to heat the fuel flow from the fuel storage tank;   a second heat exchanger where thermal energy from a heat source is input into the fuel flow from the core engine downstream of the first heat exchanger; and   a turboexpander configured to generate shaft power from expansion of the fuel flow exhausted downstream from at least one of the first heat exchanger and the second heat exchanger.   
     
     
         2 . The aircraft propulsion system as recited in  claim 1 , wherein the turboexpander is configured to receive the fuel flow downstream of the first heat exchanger and upstream of the second heat exchanger. 
     
     
         3 . The aircraft propulsion system as recited in  claim 1 , wherein the turboexpander is configured to receive the fuel flow downstream of the second heat exchanger and upstream of the first heat exchanger. 
     
     
         4 . The aircraft propulsion system as recited in  claim 1 , wherein the turboexpander is configured to receive the fuel flow downstream from the first heat exchanger. 
     
     
         5 . The aircraft propulsion system as recited in  claim 1 , further comprising a third heat exchanger where the fuel flow downstream from the first heat exchanger is further heated. 
     
     
         6 . The aircraft propulsion system as recited in  claim 5 , further comprising a valve system where the fuel flow downstream from the first heat exchanger is split such that a first portion of the fuel flow is communicated to the second heat exchanger and a second portion of the fuel flow is communicated to the third heat exchanger. 
     
     
         7 . The aircraft propulsion system as recited in  claim 6 , further comprising a bottom compressor where the first portion of the fuel flow is pressurized before communication to the second heat exchanger. 
     
     
         8 . The aircraft propulsion system as recited in  claim 6 , further comprising a bottom compressor where the fuel flow downstream from the first heat exchanger is pressurized before communication with the valve system. 
     
     
         9 . The aircraft propulsion system as recited in  claim 1 , further comprising a recuperating heat exchanger for communicating thermal energy between upstream and downstream fuel flow. 
     
     
         10 . The aircraft propulsion system as recited in  claim 1 , wherein the heat source comprises the exhaust gas flow generated from the core engine. 
     
     
         11 . The aircraft propulsion system as recited in  claim 1 , wherein the heat source comprises a system generating thermal energy that is located outside of a core flow path of the core engine. 
     
     
         12 . A gas turbine engine assembly comprising:
 a compressor, a combustor and a turbine coupled to an engine shaft, wherein a mix of air and fuel is ignited in the combustor to generate an exhaust gas flow that is expanded through the main turbine to drive the engine shaft and subsequently exhausted through an exhaust nozzle;   a propulsive fan driven by the engine shaft;   a cryogenic fuel system comprising a cryogenic fuel storage tank;   a fuel flow path where cryogenic fuel flow is circulated from upstream in a direction downstream to the combustor;   a first heat exchanger where heat input into the cryogenic fuel flow downstream of the first heat exchanger is used to heat the cryogenic fuel flow from the cryogenic fuel storage tank;   a second heat exchanger where thermal energy from a heat source is input into the cryogenic fuel flow downstream from the first heat exchanger;   a bottoming cycle system comprising a bottoming compressor configured to pressurize at least a portion of the cryogenic fuel flow exhausted from the first heat exchanger and a turboexpander configured to generate shaft power from expansion of the cryogenic fuel flow exhausted from at least one of the first heat exchanger and the second heat exchanger.   
     
     
         13 . The gas turbine engine assembly as recited in  claim 12 , further comprising a valve system where the cryogenic fuel flow exhausted from the first heat exchanger is split such that a first portion of the fuel flow is communicated to the bottoming compressor and a second portion of the fuel flow is communicated to the combustor. 
     
     
         14 . The gas turbine engine assembly as recited in  claim 13 , wherein the valve system is further configured to adjust a flow rate of the second portion of the fuel flow independent of the first portion of the fuel flow. 
     
     
         15 . The gas turbine engine assembly as recited in  claim 13 , wherein the bottoming compressor is configured to pressurize the cryogenic fuel flow before communication to the valve system. 
     
     
         16 . The gas turbine engine assembly as recited in  claim 12 , further comprising a recuperating heat exchanger for communicating thermal energy between upstream and downstream fuel flow. 
     
     
         17 . The gas turbine engine assembly as recited in  claim 12 , wherein the heat source comprises at least one of the exhaust gas flow generated from the combustor and a system generating thermal energy that is located outside of a core flow path. 
     
     
         18 . A method of assembling an aircraft propulsion system comprising assembling a core engine comprising a combustor where a cryogenic fuel is mixed with compressed air and ignited to generate an exhaust gas flow;
 assembling a propulsive fan configured to be driven by shaft power generated by the core engine;   assembling a cryogenic fuel system comprising a cryogenic fuel storage tank and a fuel flow path where a fuel flow is circulated from upstream in a downstream direction to the combustor of the core engine;   assembling a first heat exchanger where heat input into the fuel flow downstream of the heat exchanger is input into the fuel flow is used to heat the fuel flow from the cryogenic fuel storage tank;   assembling a second heat exchanger where thermal energy from a heat source is input into the fuel flow from the core engine downstream of the first heat exchanger; and   assembling a bottoming cycle system comprising a bottoming compressor configured to pressurize the fuel flow exhausted from the first heat exchanger and a turboexpander configured to generate shaft power from expansion of the fuel flow exhausted from at least one of the first heat exchanger and the second heat exchanger.   
     
     
         19 . The method as recited in  claim 18 , further comprising assembling a valve system configured to split the fuel flow exhausted from the first heat exchanger into a first portion of the fuel flow that is communicated to the bottoming compressor and a second portion of the fuel flow that is communicated to the combustor and configuring the valve system to be controlled to adjust a flow rate of the second portion of the fuel flow independent of the first portion of the fuel flow. 
     
     
         20 . The method as recited in  claim 18 , further comprising assembling the turboexpander to drive at least one of a generator, fuel pump or accessory device.